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EPC703-QFN16 Datasheet(PDF) 6 Page - Espros Photonics corp |
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EPC703-QFN16 Datasheet(HTML) 6 Page - Espros Photonics corp |
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6 / 11 page  epc700/epc702 Application Information epc700 and epc702 have two modes of operation, where the SENS pin is used to define the mode. When SENS is tied to VDD, the chip operates as a sink driver capable to sink max. 50mA at 30VDC (refer to Figure 6). The load is connected directly between V L and the OUT pin. If the current through the internal switch exceeds I SENS, the switch is turned off. If the SENS pin is at low level, the OUT pin is driven by a source driver also capable to drive 50mA into an external power transistor. This mode is used if the required output current has to be higher than 50mA, e.g. 1A and the output voltage exceeds 30VDC (refer to Figure 7). The load current is measured by monitoring the voltage drop over a resistor. If the internal switch is used, also the current measurement resistor is located internally (Figure 6). In the case of using an external power transistor as shown in Figure 7, the current measurement resistor RS has to be placed externally. If the voltage drop at RS exceeds the threshold of 200 mV, the output stage is deactivated. The timing diagrams of the signals can be found in section “Functional Description”. The IN signal must be low during power-up (tSTARTUP) for proper function of the chip. The epc70x has a built in pull down resistor, so not external active driving is needed during startup. epc700 or epc702 Using the Internal Switch Figure 6 shows the epc700/702 in the mode using the internal switch. To enable this mode, the SENS pin has to be connected to VDD. Note that the VDD of the chip and VL at the load can have a different value. The values for both VDD and VL need to be between 9.6 and 30V. The factor frt between minimum off-time and delay-time must be maintained in order not to damage the chip due to overheating. This factor has to be higher than 1,000. In the worst case scenario a peak current of approx. 0.5A is flowing from VL at 30V into the chip with a tDel set at 50μs if a short-circuit occurs. If the recovery time tminoff in this case is smaller then 50ms, the average power dissipation would exceed the safe operation condition and the device will get damaged. The diode D1 is to protect the internal switch against voltage surges when inductive loads are turned off. R1 is to protect the internal switch in case of a short circuit on the load when a very low impedance power supply is used. The voltage VL can be higher than VDD in this configuration. However, it must not be above the maximum value of 'Supply Voltage' stated in the table Electrical Characte- ristics. epc700 or epc702 Using an External Switching Transistor Figure 7 shows the operation mode using an external switch T1 in order to extend the output current/voltage drive capability. In this example, a bipolar transistor is used, whereas the base current is limited by the resistor RB. The maximum base current is 50mA. In order not to damage the chip, the user has to select the resistor RB such that chip does not need to drive more than 50mA. Other possible switches are a NPN BJT or an n-channel MOSFET. The load is turned on and off by setting the pin IN to high respectively to low level. When the load is turned on, the load current flows from VL through the resistor RS and through the transistor T1 to GND. This current creates a voltage drop over RS. The resulting voltage is applied to pin SENS, which measures the voltage drop. If it exceeds the threshold of an internal comparator, set to 200mV, the output is turned off after the given delay time tdel. If the delay time should be extended to a value above the possible settings of tdel (refer to Table 3), an RC network can added, designated as RT and CT in Figure 7. The additional time delay text can be calculated approx. as RT x CT. However, the time varies according to the current through RS. This design concept is especially useful, when a large capacitor in the load path needs to be charged. The additional delay in the over-current detection helps in such a situation. Note that the VDD of the chip and VL on the load are different in most of the applica- tions. The value of VDD must be between 9.6 and 30V. VL instead, can be on a level which is appropriate to the external switching transistor. The diode D1 is to protect the transistor T1 against voltage surges when inductive loads are turned off. © 2011 ESPROS Photonics Corporation Characteristics subject to change without notice 6 Datasheet epc700_702 - V2.2 www.espros.ch Dieter Kägi 25.05.2011 Page 1 File: Unbenannt This document is confidential and protected by law and international trades. It must not be shown to any third party nor be copied in any form without our written permission . GND GND VDD IN STATUS epc700 epc702 SENSE OUT VDD D L R L R1≥50Ω C T GND VDD IN STATUS epc700 epc702 SENSE OUT GND R T R SENSE T1 R1 V L VDD D L R L V L ≤VDD max Figure 6: epc700 or epc702 using the internal switch to drive a load of up to 50mA /30VDC Dieter Kägi 25.05.2011 Page 1 File: This document is confidential and protected by law and international trades. It must not be shown to any third party nor be copied in any form without our written permission . GND GND VDD IN STATUS epc700 epc702 SENSE OUT VDD D L R L R1≥50Ω C T GND VDD IN STATUS epc700 epc702 SENSE OUT GND R T R SENSE T1 R1 V L VDD D L R L V L ≤VDD max Figure 7: epc700 or epc702 operation mode using an external switching transistor. In case of a short-circuit in the load the turn-off delay can be extended by an external RC network. This network adds text to the internal delay tdel. |
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